1. Field of the Invention
This invention relates to a container cleanliness measurement apparatus and method, and a substrate processing system. More particularly, this invention relates to a container cleanliness measurement apparatus for use with a container for housing substrates so as to be isolated from a surrounding environment.
2. Description of the Related Art
In a semiconductor device manufacturing factory, there are installed in a clean room a plurality of substrate processing apparatuses between which semiconductor wafers (hereinafter referred to as “wafers”) are transferred. To prevent dusts floating in the clean room from adhering to wafers that are being transferred, the wafers are received in a container, for example, in an FOUP (front opening unified pod), so as to be isolated from a surrounding environment.
As shown in FIG. 9A, the FOUP 90 is a container which is extruded into a U-shape as seen from above. The FOUP 90 includes a body 91 having a curved side surface and an opposite open side surface, and a lid 92 disposed to face an opening in the open side surface of the body 91 and adapted to open and close the opening. The lid 92 has a seal rubber of NBR or the like and is in close contact at its periphery with the body 91 via the seal rubber. The body 91 and the lid 92 are made of ABS or other resin. The body 91 has a plurality of plate-like carriers 94 extending from an inner wall surface of the body 91 toward a center part thereof and disposed parallel to one another (FIG. 9B).
The carriers 94 hold outer peripheral portions of rear surfaces of a plurality of wafers W when the wafers are housed in the FOUP 90. Thus, the wafers W are housed in the FOUP 90 so as to extend parallel to one another.
The present inventors confirmed the following. When plasma processing such as etching is performed on a wafer W, particles are adhered to a rear surface of the wafer W and deposits are adhered to a bevel portion thereof. Particles and deposits separated from wafers of a certain lot housed in the FOUP 90 are sometimes adhered to an inner wall surface of the body 91 and to the carriers 94. In a state that wafers W of the next lot are housed in the FOUP 90, the particles, etc. adhered to the inner wall surface of the body 91 and to the carriers 94 are separated therefrom and adhered to (secondarily contaminate) the wafers W of the next lot.
The particles, etc. adhered to the wafers W function as a micromask in etching and CVD processing, which causes problems with semiconductor devices. To obviate this, there has been developed a cleaning system for cleaning an FOUP in which processing on wafers of a certain lot is completed (see, for example, the following online article).
“FOUP cleaning system” on the web page of Technovision Inc., searched Aug. 6, 2007 on the Internet <URL:http://www.techvision.co.jp/products/foup.htm>
In this cleaning system, the entire FOUP 90 is cleaned using pure water and then dried to remove particles, etc. adhered to the inner wall surface of the FOUP and to the carriers 94.
Conventionally, however, whether or not the FOUP 90 must be cleaned is determined based only on the use time of the FOUP. Therefore, the FOUP 90 is cleaned even when substantially no particles, etc. are adhered to the inner wall surface of the FOUP 90 and to the carriers 94, i.e., even when there is substantially no possibility of secondary contamination. This results in a reduction in operation efficiency of the FOUP 90, which poses a problem.
In some cases, the FOUP 90 cannot be adequately cleaned with the cleaning system. Nevertheless, there is no means for confirming whether or not adequate cleaning has been performed. When the FOUP 90 not adequately cleaned is used again, there occurs a problem of secondary contamination.
The above problems are caused by the inability of accurate measurement of the cleanliness of the FOUP 90, i.e., the inability of measurement of an amount of particles adhered to the inner wall surface of the FOUP 90 and to the carriers 94.